Analyzer system and optical filtering

ABSTRACT

A gas analyzer system includes an optical source, an optical filter assembly, a controller, and an analyzer. The optical source generates an optical signal. The optical filter assembly includes different optical filters in which to filter the optical signal. During operation, the controller selects sequential application of each of the different optical filters in a path of the optical signal to modulate the optical signal using different frequency bands of optical energy. The modulated optical signal passes through an unknown sample. The optical analyzer analyzes the modulated optical signal after passing through the sample to detect which types of multiple different gases are present in the sample.

RELATED APPLICATION

This application claims priority to United States Provisional patent application entitled “FLUID ANALYZER SYSTEM” (Attorney Docket No. TEC07-04(TEI)p) having assigned Ser. No. 61/030,475, filed on Feb. 21, 2008, the entire teachings of which are incorporated herein by this reference.

This application is related to United States patent application entitled “GAS ANALYZER SYSTEM” (Attorney Docket No. TEC07-05(TEI)) filed on the same day as the present application, the entire teachings of which are incorporated herein by this reference.

BACKGROUND

Emissions from fossil fuel combustion facilities, such as flue gases of coal-fired utilities and municipal solid waste incinerators, typically include multiple types of gases. For example, emissions can include gases such as CO₂, NO₂, SO₂, etc.

Many countries regulate emissions of the different types of waste gases because of potential environmental hazards posed by such harmful emissions. Accordingly, many facilities that generate or potentially generate harmful gas emissions need to employ multiple gas analyzers systems to ensure that emitted gases are compliant with corresponding regulations. Operating and maintaining each of the different gas analyzer systems can be expensive.

Each of the different types of gases has unique optical absorption characteristics. These unique characteristics enable a corresponding gas analyzer system to positively identify whether a particular type of gas is present in a gas sample.

One way to quantify a type of gas present in an unknown gas sample is the application of Beer's law. In general, Beer's law defines an empirical relationship that relates the absorption of light to properties of the material through which the light is traveling. In other words, different materials absorb different frequencies of light energy. By passing of optical energy through a gas sample and detecting which frequencies of optical energy are absorbed by the gas sample, it is possible to determine what type of gas is present in the gas sample. The amount of absorption can indicate a concentration of a respective gas.

One conventional gas analyzer system includes an optical source that generates an optical signal for passing through a sample gas. Such an analyzer also includes a so-called optical filter wheel and a so-called chopper wheel. The optical filter wheel and the chopper are both disposed in a path of the optical signal.

The optical filter wheel includes a number of different optical filters, each of which passes only a single frequency band of light energy. Depending on which filter is disposed in a path of the optical signal, it is known what frequency band of light is being passed through the sample. An optical detector measures how much optical energy passes though the sample.

The chopper wheel includes multiple windows or cut-outs separated by opaque regions that block light. The chopper wheel is also placed in a path of the optical signal such that a position of the chopper wheel dictates whether any of the optical signal passes through the gas sample or is blocked by an opaque region. As the chopper wheel spins, it blocks and passes optical energy through the sample to a detector.

During operation, a conventional gas analyzer system produces modulated light by setting the filter wheel in a position so that the optical signal passes through a selected filter in the optical wheel. When the selected filter is in such a position, a controller spins the chopper wheel to repeatedly block and pass the optical signal through the gas sample as discussed above. Application of the chopper wheel results in modulation of a single frequency band of optical energy depending on which filter on the filter wheel has been chosen to be “chopped” or modulated. Accordingly, a controller can produce a modulated optical signal using a two-wheel assembly including a chopper wheel and filter wheel.

SUMMARY

Conventional ways of generating a modulated optical signal suffer from a number of deficiencies. For example, the conventional two-wheel assembly as discussed above is prone to failure because it includes many moving parts. In particular, such an assembly includes a filter wheel and a chopper wheel that operate independently of each other and, thus, require separate driver control logic and motors.

Embodiments herein include a unique way to produce a modulated optical signal and collect data for detecting a presence of different types of matter in a sample chamber.

More specifically, in one embodiment, a gas analyzer system includes an optical source, an optical filter, a controller, and an analyzer. The optical source generates an optical signal. The optical filter assembly includes different optical filters in which to filter the optical signal. The controller is configured to select sequential application of each of the different optical filters in a path of the optical signal to modulate the optical signal. The optical analyzer analyzes the modulated optical signal passing through a sample to detect which of one or more types of matter are present in the sample.

By way of a non-limiting example, the matter can include different types of gases, liquids, or solids present in the sample.

In addition to having an ability to detect different types of gases present in the sample, an example analyzer system as described herein can determine a concentration of multiple gases present in the sample based on how much of the modulated optical signal is absorbed by the sample at different optical energies.

It is possible that two or more of the different gases present in the sample may absorb optical energy in a common frequency band of the modulated optical signal due to interference. This complicates the task of detecting which types of gases may be present in the sample. Thus, merely knowing that a gas sample absorbs a single frequency of light energy may not be enough information to determine which gas is present in the sample. To discern between different gases, the optical filter assembly can include multiple filters in which to measure absorption of optical energy. Depending on how much energy is absorbed in different optical frequency bands, the gas analyzer system according to embodiments herein can identify concentrations of different types of gases in a sample even though there happens to be absorbance interference amongst the gases.

In further embodiments, the optical filter assembly can be an optical filter wheel including the different optical filters, each of which is separated by opaque partitions that block the optical signal from passing through the sample.

When disposed in a path of the optical signal, the controller can initiate spinning the wheel to produce a modulated signal of different optical energy frequency bands. For example, a filter wheel according to embodiments herein can include a first filter, a second filter, a third filter, etc. In accordance with embodiments as discussed above, between each filter pair is an opaque region that blocks the optical energy. Each filter passes different frequency bands of optical energy. The controller can be configured to rotate the optical wheel to each of multiple successive positions including a first position, a second position, a third position, a fourth position, a fifth position, etc. to produce the modulated optical signal.

When in the first position, the first filter is disposed in a path of the optical signal enabling the optical signal to pass through the first optical filter and the sample to the analyzer.

When in the second position, an opaque region of the optical filter wheel is disposed in a path of the optical signal to block the optical signal from passing through the sample.

When in the third position, the second filter is disposed in a path of the optical signal enabling the optical signal to pass through the second optical filter and the sample to the analyzer.

When in the fourth position, another opaque region of the optical filter wheel is disposed in a path of the optical signal to block the optical signal from passing through the sample.

When in the fifth position, the third filter is disposed in a path of the optical signal enabling the optical signal to pass through the first optical filter and the sample to the analyzer. Sequentially setting the optical filter wheel in these positions as discussed herein produces the modulated optical signal for passing through the sample to detect the presence of different gases.

This process can be repeated for any number of filters on the optical filter wheel such that the controller generates the modulated optical signal based on positioning different optical filters in a path of the optical signal. As each different filter is sequentially disposed in the optical path, the analyzer collects absorption information for the frequency band. The transition from one filter to a next filter serves as a way of modulating the optical signal.

Modulating the optical signal as described herein enables the analyzer to collect absorption data in a different manner than as discussed above for the conventional two-wheel assembly including a chopper wheel. For example, the conventional two-wheel assembly lends itself to repeated sampling of the optical signal for a single filter of the filter wheel assembly based on use of the chopper wheel. In contradistinction to the conventional two-wheel assembly, embodiments herein enable more efficient serial collection of absorption data in a serial manner via modulation without use of a chopper wheel.

Techniques herein are well suited for use in applications such as those supporting detection of different types of gases in a gas sample. However, it should be noted that configurations herein are not limited to such use and thus configurations herein and deviations thereof are well suited for use in other environments as well.

Note that each of the different features, techniques, configurations, etc. discussed herein can be executed independently or in combination. Accordingly, the present invention can be embodied and viewed in many different ways.

Also, note that this summary section herein does not specify every embodiment and/or incrementally novel aspect of the present disclosure or claimed invention. Instead, this summary only provides a preliminary discussion of different embodiments and corresponding points of novelty over conventional techniques. For additional details and/or possible perspectives or permutations of the invention, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure as further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments herein as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the embodiments, principles and concepts.

FIG. 1 is an example diagram of an analyzer system according to embodiments herein.

FIG. 2 is an example diagram illustrating an optical filter assembly according to embodiments herein.

FIG. 3 is an example diagram illustrating detected intensities of light for different frequency bands according to embodiments herein.

FIG. 4 is an example diagram illustrating collected sample data according to embodiments herein.

FIG. 5 is an example graph illustrating absorption of energy associated with carbon dioxide over a range of wavelengths.

FIG. 6 is an example graph illustrating absorption of energy associated with carbon monoxide over a range of wavelengths.

FIG. 7 is an example graph illustrating energy absorption at different wavelengths for multiple different gas samples.

FIG. 8 is an example block diagram of a computer system configured with a processor and related storage to execute different methods according to embodiments herein.

FIGS. 9 and 10 are example flowcharts illustrating methods according to embodiments herein.

DETAILED DESCRIPTION

Now, more specifically, FIG. 1 is an example diagram of an analyzer system 100 according to embodiments herein. As shown, analyzer system 100 includes a user 108, an optical source 110, optical signal 115, optical filter assembly 120, modulated optical signal 125, chamber 129, detector assembly 135, repository 180, sample data processor 142, and display screen 130. Optical filter assembly 120 includes multiple filters 122 such as filter 122-1, filter 122-2, filter 122-3, filter 122-4, filter 122-5, filter 122-6, filter 122-7, filter 122-8, filter 122-9, filter 122-10, etc. Chamber 129 includes inlet 127, outlet 128, and reflectors 131-1 and 131-2. Display screen 130 displays report 145 for viewing by user 108. Detector assembly 135 includes detector 136 and monitor circuit 137.

In general, analyzer system 100 analyzes absorption characteristics of sample 126 as it passes from inlet 127 through chamber 129 to outlet 128. The analyzer system 100 passes the modulated optical signal 125 through the sample 126 to identify a presence and/or concentrations of multiple different target gases such as H₂O (water), CO (carbon monoxide), CO₂ (carbon dioxide), NO (nitric oxide), NO₂ (nitrogen dioxide), SO₂ (sulfur dioxide), N₂O (nitrous oxide), CH₄ (methane), HC (hydrocarbons), etc.

By way of a non-limiting example, the inlet 127 of chamber 128 can be configured to receive gas sample 126 from a smokestack. In such an embodiment, the analyzer system 100 measures combustion by-products in sample 126 using a unique method employing non-dispersive infrared (IR) absorbance spectroscopy.

The basis of analyzing sample 126 according to one embodiment is use of Beer-Lambert's Law. As mentioned above, this law defines a linear relationship between the concentration of a gas of interest and the amount of energy it absorbs. Via this technique, the gas analyzer 140 determines the presence and/or concentration of matter such as individual pollutants in the sample 126 based on the capacity of the compounds to absorb infrared energy of a specific wavelength.

During operation, optical source 110 generates optical signal 115. In one embodiment, and by way on a non-limiting example, the optical source generates optical signal 115 in an infrared spectrum such as a broad range of optical wavelengths between 1.5 and 7.5 micrometers. The optical source 115 can be a device such as semiconductor device, a glowing metal filament heated to a temperature of several hundred degrees C., etc.

In one embodiment, the optical detector 136 is a pyroelectric detector device such as the Selex detector Type #5482 (available from SELEX S&AS, PO Box 217, Millbrook Industrial Estate, Southampton, Hampshire, UK).

In accordance with another embodiment, the detector device is a lead-selenide device such as the SensArray detector, part number SA-432-386T (available from SensArray Infrared, Burlington, Mass. 01803).

As its name suggests, filter controller 155 changes which of multiple optical filters 122 is aligned in a path of the optical signal 115 for passing of a limited frequency band of the optical signal 115 through sample 126 to detector 136. The filter controller 155 produces the modulated optical signal 125 by rotating an optical filter assembly 120 to each of multiple successive positions in which the optical filters 122 pass different frequency bands of optical energy through the sample 126.

As an example, optical filter assembly 120 can be a filter wheel that spins in response to input by the filter controller 155.

More specifically, the filter controller 155 rotates optical filter assembly 120 so that optical filter 122-1 of the optical filter assembly 120 initially lies in the path of the optical signal 115. When in such a position, the filter 122-1 absorbs certain frequencies in the optical signal 115 and passes other frequencies of the optical signal 115 to sample 126 in chamber 129.

As the optical filter assembly 120 rotates further, filter 122-1 moves out of the path of optical signal 115. The opaque partition of the optical filter assembly 120 between filter 122-1 and filter 122-2 then temporarily blocks the optical signal 115 so that substantially little or no optical energy passes through the sample 126 in chamber 129 to detector 126.

The filter controller 155 continues to rotate optical filter assembly 120 so that optical filter 122-2 aligns in the path of the optical signal 115. When in such a position, the filter 122-2 absorbs certain frequencies in the optical signal 115 and passes other frequencies of the optical signal 115 to sample 126 in chamber 129.

As the optical filter assembly 120 rotates further, filter 122-2 moves out of the path of optical signal 115. The opaque partition of the optical filter assembly 120 between filter 122-2 and filter 122-3 then temporarily blocks the optical signal 115 so that substantially little or no optical energy passes through the sample 126 in chamber 129.

The filter controller 155 continues to rotate optical filter assembly 120 so that optical filter 122-3 of the optical filter assembly 120 lies in the path of the optical signal 115. When in such a position, the filter 122-3 absorbs certain frequencies in the optical signal 115 and passes other frequencies of the optical signal 115 to sample 126 in chamber 129.

Based on repeating the above sequence of blocking and filtering different portions of the optical signal 115 over time, analyzer system 100 produces modulated optical signal 125 by multiplexing different frequency bands of the optical signal 115 through the sample. Each filter 122 can pass one or more frequency bands or channels of optical energy to the optical detector 136.

As mentioned above, the analyzer system 100 passes the (multi-frequency) modulated optical signal 125 through sample 126. Depending on how much energy in the different energy bands is absorbed by the sample, the analyzer 140 detects types of gas present in the chamber 126 as well as a concentration of the detected gases.

By way of a non-limiting example, the filter controller 155 can initiate spinning the optical filter assembly 120 at a rate such as thirty rotations per second. In such an embodiment, assuming there are twelve filters on the optical filter assembly 120, the detector 136 and sampling circuit 137 collects three hundred sixty intensity samples or thirty samples per each filter for each second.

A rate of rotating the optical filter assembly 120 to collect data can vary depending on such factors as how many filters are presenting the optical filter assembly 120, the ability of the detector 136 to take a reading, etc.

The chamber 129 can include reflector 131-1 and reflector 131-2 to increase the optical path length of the modulated optical signal 125 as it passes through the sample 126. Increasing the effective optical path length of the modulated optical signal 125 in the chamber 129 enables greater absorption of the modulated optical signal 125 when a target gas happens to be present in the chamber 129. This results in more accurate gas type determinations and/or more accurate gas concentration readings.

By way of a non-limiting example, the reflectors 131 can be configured as a multi-pass cell in which the optical signal repeatedly reflects off reflector 131-1 and 131-2 prior to striking detector 136.

After passing through chamber 129, a portion of the modulated optical signal 132 not absorbed by the sample 126 strikes detector assembly 136. By way of non-limiting example, an output signal 305 such as on output voltage of the detector 136 varies depending on how much energy is present in the optical signal 132. Monitor circuit 137 can include an amplifier and A/D circuit (e.g., analog to digital converter circuit) to measure a strength of the received optical signal 132. For example the monitor circuit 137 samples the intensity of the detector 136 to produce sample data 138. For example, detector assembly 135 then stores intensity readings associated with optical signal 132 as sample data 138 in repository 180.

By way of a non-limiting example, an output signal 305 such as the output voltage of the detector 136 varies depending on how much energy is present in the optical signal 132. Monitor circuit 137 can include an amplifier and A/D circuit (e.g., analog to digital converter circuit) to measure a strength of the received optical signal 132.

In an example embodiment, the detector assembly 135 can be configured to detect peak values and trough values associated with the optical signal 132 as illustrated in FIG. 3. As will be discussed later in this specification, peaks and troughs provide a relative measure of how much of the optical energy at the different frequency bands has been absorbed by the sample 126.

The sample data processor 142 of analyzer 140 processes the sample data 138 such as peak and trough information at the different frequency bands to identify which, if any, types of gases are present in the chamber 129 as well as concentrations of the gases. Via report 145 on display screen 130, the analyzer 140 can indicate the different types of gases and concentrations in the sample 126 for viewing by user 108.

A benefit of sequentially collecting data in the different frequency bands is the ability to more accurately detect a presence of fast moving gases in chamber 126. For example, conventional methods include setting a filter in a path of an optical signal and chopping the frequency with a so-called chopper wheel as discussed above. In such an embodiment, a fast moving gas of a particular type may not be detected because the conventional analyzer did not sample the appropriate frequency bands while the fast passing gas was present in a sample chamber. Embodiments herein include sequentially collecting data from different frequency bands. In such embodiments, a fast passing gas in the chamber 129 is more likely to be detected by the analyzer 140 because the frequency bands are changed more frequently.

FIG. 2 is a diagram illustrating an example filter assembly 120 for filtering optical signal 115 and producing modulated optical signal 125 according to embodiments herein. As shown, optical filter assembly 120 includes multiple filters 122 including reference filter 122-1, reference filter 122-2, filter 122-3, filter 122-4, filter 122-5, filter 122-6, filter 122-7, filter 122-8, filter 122-9, filter 122-10, filter 122-11, and filter 122-12. Opaque regions 220 such as opaque region 220-1, opaque region 220-2, opaque region 220-3, block optical energy from passing through sample 126.

Note that use of twelve filters is shown by way of example only and that optical filter assembly 120 can include any practical number of filters.

Each of the filters 122 can be chosen so that it is possible for the analyzer 140 to identify which, if any, types of the target type gases are present in the sample 126 passing through the chamber 129. As previously discussed, the target gases can include gases such as H₂O (water), CO (carbon monoxide), CO₂ (carbon dioxide), NO (nitric oxide), NO₂ (nitrogen dioxide), SO₂ (sulfur dioxide), N₂O (nitrous oxide), CH₄ (methane), HC (hydrocarbons), etc.

By way of a non-limiting example, the filters 122 can be configured as follows:

Each of reference filter 122-1 and reference filter 122-2 can be configured to have a center wavelength of approximately 3.731 micrometers +/−2 percent. The filter 122-1 can have an FWHM (Full Width at Half Maximum) of 0.08 micrometers. Of course, these are examples only and the actual filters can vary depending on a respective application.

Assuming that the center wavelength of filter 122-1 is 3.731 micrometers, when the filter 122-1 is positioned in a path of the optical signal 115, the filter 122-1 passes a wavelength band or range of energy centered around 3.731 micrometers.

In one embodiment, the center wavelength value of filter 122-1 such as 3.731 micrometers is chosen such that the filter passes a range of energy wavelengths that are not absorbed by any of the target gases except water, which tends to absorb energy in every channel. Use of such reference channels (i.e., filter 122-1 and filter 122-2) serve as a way to correct for drift associated with other channels in the analyzer system 100. Drift can be caused by factors such as changes in the intensity of the optical signal 115 produced by 115 over time, changes in the detector and its ability to detect optical signal 132 over time, etc. If used for correction of drift, the readings produced by the analyzer system 100 typically will be more accurate.

Disposing of the reference filters 122-1 and 122-2, one after the other in a sampling sequence, enables the analyzer system 100 to obtain a more accurate reference reading because the first reference filter 122-1 establishes a good pre-sample for taking a following reading with filter 122-2.

Filter 122-3 can be configured to have a center wavelength of approximately 2.594 micrometers +/−2 percent. The filter 122-2 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-3 is 2.594 micrometers, when the filter 122-3 is positioned in a path of the optical signal 115, the filter 122-3 passes a wavelength band or range of energy centered around 2.594 micrometers. This frequency band is at least partially absorbed by H₂O when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: CO (carbon monoxide), CO₂ (carbon dioxide), and N₂O (nitrous oxide).

Filter 122-4 can be configured to have a center wavelength of approximately 4.630 micrometers +/−2 percent. The filter 122-4 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent.

Assuming that the center wavelength of filter 122-4 is 4.630 micrometers, when the filter 122-4 is positioned in a path of the optical signal 115, the filter 122-4 passes a wavelength band or range of energy centered around 4.630 micrometers. This frequency band is at least partially absorbed by CO (carbon monoxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water) and N₂O (nitrous oxide).

Filter 122-5 can be configured to have a center wavelength of approximately 4.843 micrometers +/−2 percent. The filter 122-5 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-5 is 4.843 micrometers, when the filter 122-5 is positioned in a path of the optical signal 115, the filter 122-5 passes a wavelength band or range of energy centered around 4.843 micrometers. This frequency band is at least partially absorbed by CO₂ (carbon dioxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: CO (carbon monoxide), NO (nitric oxide), and SO₂ (sulfur dioxide).

Filter 122-6 can be configured to have a center wavelength of approximately 5.25 micrometers +/−2 percent. The filter 122-6 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-6 is 5.25 micrometers, when the filter 122-6 is positioned in a path of the optical signal 115, the filter 122-6 passes a wavelength band or range of energy centered around 5.25 micrometers. This frequency band is at least partially absorbed by NO (nitric oxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water), CO₂ (carbon dioxide), and NO₂ (nitrogen dioxide).

Filter 122-7 can be configured to have a center wavelength of approximately 6.211 micrometers +/−2 percent. The filter 122-7 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-7 is 6.211 micrometers, when the filter 122-7 is positioned in a path of the optical signal 115, the filter 122-7 passes a wavelength band or range of energy centered around 6.211 micrometers. This frequency band is at least partially absorbed by NO₂ (nitrogen dioxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water), CO (carbon monoxide), NO (nitric oxide), SO₂ (sulfur dioxide), and N₂O (nitrous oxide).

Filter 122-8 can be configured to have a center wavelength of approximately 8.696 micrometers +/−2 percent. The filter 122-8 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-8 is 8.696 micrometers, when the filter 122-8 is positioned in a path of the optical signal 115, the filter 122-8 passes a wavelength band or range of energy centered around 8.696 micrometers. This frequency band is at least partially absorbed by SO₂ (sulfur dioxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: CO (carbon monoxide), NO₂ (nitrogen dioxide), and N₂O (nitrous oxide).

Filter 122-9 can be configured to have a center wavelength of approximately 7.831 micrometers +/−2 percent. The filter 122-9 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-9 is 7.831 micrometers, when the filter 122-9 is positioned in a path of the optical signal 115, the filter 122-9 passes a wavelength band or range of energy centered around 7.831 micrometers. This frequency band is at least partially absorbed by N₂O (nitrous oxide) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: SO₂ (sulfur dioxide).

Filter 122-10 can be configured to have a center wavelength of approximately 3.236 micrometers +/−2 percent. The filter 122-10 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-10 is 3.236 micrometers, when the filter 122-10 is positioned in a path of the optical signal 115, the filter 122-10 passes a wavelength band or range of energy centered around 3.236 micrometers. This frequency band is at least partially absorbed by CH₄ (methane) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water), SO₂ (sulfur dioxide), and N₂O (nitrous oxide).

Filter 122-11 can be configured to have a center wavelength of approximately 3.367 micrometers +/−2 percent. The filter 122-11 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-11 is 3.367 micrometers, when the filter 122-11 is positioned in a path of the optical signal 115, the filter 122-11 passes a wavelength band or range of energy centered around 3.367 micrometers. This frequency band is at least partially absorbed by HC (hydrocarbons) when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water), NO₂ (nitrogen dioxide), SO₂ (sulfur dioxide), and N₂O (nitrous oxide).

Filter 122-12 can be configured to have a center wavelength of approximately 3.896 micrometers +/−2 percent. The filter 122-12 can also have an FWHM (Full Width at Half Maximum) of +/−15 percent of the center wavelength.

Assuming that the center wavelength of filter 122-12 is 3.896 micrometers, when the filter 122-12 is positioned in a path of the optical signal 115, the filter 122-12 passes a wavelength band or range of energy centered around 3.896 micrometers. This frequency band is at least partially absorbed by N₂O when present in the sample 126. Other gases that absorb energy in this range, and which are possibly present in sample 126, include: H₂O (water), NO₂ (nitrogen dioxide) and SO₂ (sulfur dioxide).

Note again that the center frequencies and frequency bands as discussed above for each of the filters 122 is presented as an example only and that these values can vary depending on the embodiment or which types of gases are to be detected in sample 126 passing through chamber 129. Generally, filters 122 can be any values that allow passing of bands of optical energy that can be absorbed by sample 126 and aid in discerning which of multiple gases are present in the sample 126.

FIG. 3 is an example diagram illustrating intensities of optical energy for different frequency bands according to embodiments herein. As shown, detector 136 senses a magnitude of light energy in a respective frequency band depending on which filter is in the path of optical signal 115. Signal 305 such as an output voltage of the detector 136 represents a measure of how much optical energy is detected by detector 136. As previously discussed, sample 126 absorbs a certain portion of optical energy passed by a respective filter depending on which of one or more types of gases are present in sample 126.

Between time T0 and time T1, the light-blocking region of optical filter assembly 120 between filter 122-12 and filter 122-1 passes the path of optical signal 115. Because the signal is being blocked during such time, the intensity of signal 305 decreases.

Between time T1 and time T2, the reference filter 122-1 passes the path of optical signal 115. Because a respective frequency band of optical signal 115 passes though filter 122-1 during such time, the intensity of signal 305 increases. As previously discussed, the amount of optical energy detected by detector 136 will vary depending on drift or other undefined fluctuations in the system hardware. In one embodiment, one or more reference filters of the optical filter assembly have a center wavelength selected to minimize absorbance due to flue gas/sample.

Between time T2 and time T3, the light-blocking region or opaque region of optical filter assembly 120 between filter 122-1 and filter 122-2 passes the path associated with optical signal 115. Because the optical signal 115 is being blocked during such time, the intensity of signal 305 decreases.

Between time T3 and time T4, the reference filter 122-2 passes the path of optical signal 115. Because a respective frequency band of optical signal 115 passes though filter 122-2 during such time, the intensity of signal 305 increases.

Between time T4 and time T5, the light-blocking region or opaque region of optical filter assembly 120 between filter 122-2 and filter 122-3 passes the path of optical signal 115. Because the optical signal 115 is blocked during such time, the intensity of signal 305 decreases.

Between time T5 and time T6, filter 122-3 passes the path of optical signal 115. Because a respective frequency band of optical signal 115 passes though filter 122-3 during such time, the intensity of signal 305 increases. As previously discussed, the amount of optical energy detected by detector 136 will vary depending on how much of the optical signal is absorbed by sample 126.

Eventually, the analyzer 140 repeats the same sequence of filtering for each following cycle 2, 3 and so on. In one embodiment, during this process of repeatedly blocking and passing of the optical signal 115 over time, the monitor circuit 137 samples signal 305 to produce sample data 138 as in FIG. 4. An intensity reading for a given filter 122 can be a measure between a peak and subsequent valley or between a valley and subsequent peak of signal 305. Or alternately, the intensity can be measured by tracking the rate at which the signal changes when optical filters and opaque areas sequentially pass in front of the source.

For example, as previously discussed and as shown in FIG. 3, signal 305 increases between time T1 and time T2. The monitor circuit 137 can be configured to measure the optical energy in a frame such as when filter 122-1 passes in a path of optical signal 115 by repeated sampling of signal 305 to identify the lowest value of the signal 305, which occurs around time T1. The identified low value represents a valley and relative “zero” of the detector 136 for filter 122-1. The monitor circuit 137 also monitors signal 305 in the frame to identify a subsequent highest value of the signal 305, which occurs at around time T2. The high value represents a peak for filter 122-1. A difference in the signal 305 values between this peak and the valley pair represents a measure of how much optical energy is detected by the detector 136 for the given filter.

Signal 305 increases between time T3 and time T4. The monitor circuit 137 can be configured to measure the optical energy in a frame such as when filter 122-2 passes in a path of optical signal 115 by repeated sampling of signal 305 to identify the lowest value of the signal 305, which occurs around time T3. The identified low value represents a valley and relative “zero” of the detector 136 for filter 122-2. The monitor circuit 137 also monitors signal 305 to identify a subsequent highest value of the signal 305, which occurs at around time T2. The high value represents a peak for filter 122-2. A difference in the signal 305 between this peak and the valley pair represents a measure of how much optical energy is detected by the detector 136 for filter 122-2.

This monitor circuit 137 can be configured to repeat sampling of signal 305 for each of the different filters 122 on a continuous basis so that the analyzer system 100 continuously monitors the presence of different gases in sample 126 as it passes from inlet 127 through chamber 129 to outlet 128. Note again that measuring the optical energy between peak-valley pairs or valley-peak pairs to determine an absorbance of optical energy is shown by way of a non-limiting example only and that the signal 305 can be processed in a number of different ways to detect how much of the optical signal 115 passes through the sample 126 and/or how much is absorbed by the sample 126.

FIG. 4 is an example diagram illustrating sample data 138 according to embodiments herein. As shown, sample data 138-1 includes intensity readings associated with signal 305 for each of the filters 122 for cycle #1, sample data 138-2 includes intensity readings associated with signal 305 for each of the filters 122 for cycle #2, and so on. Sample data such as data 11, data 12, etc. for each successive filter 122 represents data collected by monitor circuit 137.

In one embodiment, data sample 138-1 can include sample information collected during cycle #1. For example, data 11 can include a pair of peak-valley readings for reference filter 122-1 in cycle #1, data 12 can include a pair of peak-valley readings for reference filter 122-2 in cycle #1, data 13 can include a pair of peak-valley readings for filter 122-3 in cycle #1, and so on.

In furtherance of such an embodiment, data sample 138-2 can include sample information collected during cycle #2. For example, data 21 can include a pair of peak-valley readings for reference filter 122-1 in cycle #2, data 22 can include a pair of peak-valley readings for reference filter 122-2 in cycle #2, data 23 can include a pair of peak-valley readings for filter 122-3 in cycle #2, and so on.

In this way, the monitor circuit 137 can store sample data for each of the cycles.

To reduce the amount of data stored in repository 180, the monitor circuit 137 can store sample data 138 in any of multiple different ways. For example, in one embodiment, the monitor circuit 137 collects the peak and valley values for each of the different filters 122 for cycle #1 and stores the sample data in repository 180. In following cycle #2, the monitor circuit 137 collects peak and valley values for each of the different filters 122 for cycle #2 and adds the collected peak and valley values for cycle #2 to those for cycle #1. The monitor circuit 137 repeats this process of collecting and summing the sample data such that, after K cycles, the sample data 138 in repository 180 includes a summation of K peak samples and a summation of K valley samples for filter 122-1, a summation of K peak samples and a summation of K valley samples for filter 122-2, a summation of K peak samples and a summation of K valley samples for filter 122-3, a summation of K peak samples and a summation of K valley samples for filter 122-4, and so on.

As previously discussed, after collection of the sample data 138, the analyzer 140 (FIG. 1) uses the collected sample data 138 to identify which type of matter such as gases are present in sample 126 and/or a concentration of the gases.

FIG. 5 is an example graph 500 illustrating absorption of energy associated with carbon monoxide over a range of wavelengths. As shown, carbon monoxide absorbs optical energy in the range of optical wavelengths approximately between 4.4 and 4.8 micrometers.

FIG. 6 is an example graph 600 illustrating absorption of energy associated with carbon dioxide over a range of wavelengths. As shown, carbon dioxide absorbs optical energy in the range of optical wavelengths approximately between 4.2 and 4.5 micrometers.

FIG. 7 is an example graph 700 illustrating energy absorption at different wavelengths for multiple different gases such as gas X, gas Y, and gas Z, potentially present in sample 126 passing through chamber 129. Note that this is only an example illustration of different gases and how they can absorb optical energy in the same wavelengths and thus “interfere” with each other.

As illustrated, certain gases can absorb optical energy at around the same wavelengths. For example, gas Y and gas Z both absorb optical energy in a range of wavelength values around wavelength W2. Also, gas Y and gas Z both absorb optical energy in a range of wavelength values around wavelength W3.

The following discussion presents an example of how to convert detected optical intensity values such as those in sample data 138 to one or more corresponding concentration measurements of gases present in sample 126. The first step is to determine the amount of energy that was absorbed by the gas sample. This is called the Absorbance, and it is defined as the log of the ratio of the intensity measured when there is no sample present (the Zero Intensity) divided by the intensity measured when the sample is present (Sample Intensity).

A=In(I _(o) /I _(s)),  (Equation 1)

where A is the absorbance, I_(o) is the intensity measured while sampling high purity zero air, and I_(s) the intensity measured while sampling the gas of interest.

As long as you hold other parameters constant, the absorbance is a direct measure of concentration. Also, absorbance values are additive, so if two different gases both cause some attenuation or absorbance of the modulated optical signal 125 for a given filter 122, the total absorbance at that wavelength is the sum of the individual absorbance for each of the gases. This is referred to as interference. Analyzer 140 corrects for cross interferences between channels as discussed below.

To more accurately measure absorbance of the modulated optical signal 125, the analyzer 140 can be calibrated in accordance with a calibration procedure that establishes the relationship between the measured absorbance and the concentration of the target compound in the sample 126.

In one embodiment, the calibration procedure includes filling the chamber 129 with clean, so-called “zero” air that does not contain the target compound (Absorbance=0). The analyzer 140 records the detected signal for such a gas. In one embodiment, calibration includes calibrating the analyzer 140 at each of multiple different concentrations for each gas of interest that may be present in sample 126.

According to Beer's Law:

A=εbC,  (equation 2)

where A is absorbance, ε is the absorptivity of the gas of interest, b is the sample pathlength as a result of reflections between reflectors 131, and C is the concentration of the gas of interest.

Absorbance readings increase proportionally for increased concentrations of the target compound. In practice, some deviation from linearity may be observed.

As mentioned above, the analyzer 140 can be calibrated using multipoint calibration, using high purity zero air and a series of different concentration of span gases in a factory setting.

In the field, it may be difficult for an average user to perform this type of calibration. Thus, field calibration procedures may be different than factory calibration procedures. A so-called field zero procedure or calibration performed in the field can be similar to the factory zero as discussed above, except there is no assumption that the so-called “zero” air will be free of water. Also, instead of calibrating the analyzer 140 via testing of multiple span concentrations for each target gas, the calibration procedure can include measuring a single target sample at a known concentration as the non-linearity detected during the factory calibration is repeatable.

As previously discussed, the reference wavelength for filter 122-1 and filter 122-2 is selected at a point in the optical spectrum where none of the possible target gases in the sample 126 is expected to cause absorbance. Changes in the intensity of the modulated optical signal 125 measured at the reference wavelength are assumed to occur because of fluctuations in behavior of the hardware such as the source 110 and detector 136 and are assumed to occur to the same degree in both the reference channels and sample channels. Reference channels refer to sampling of the modulated optical signal 125 via use of filter 122-1 and filter 122-2. Sample channels refer to sampling of the modulated optical signal 125 via use of filter 122-3, filter 122-4, etc. By recording the ratio of sample signal to reference signal (S/R), the impact of instrument drift or random interferences can be reduced.

FIG. 8 is a block diagram of an example architecture of a respective computer system 810 such as one or more computers, processes, etc., for implementing analyzer 140 according to embodiments herein. Computer system 810 can include one or more computerized devices such as personal computers, workstations, portable computing devices, consoles, network terminals, networks, processing devices, etc.

Note that the following discussion provides a basic example embodiment indicating how to carry out all or portions of the functionality associated with the analyzer 140 as discussed above and below. However, it should be noted again that the actual configuration for carrying out the analyzer 140 can vary depending on a respective application. For example, as previously discussed, computer system 810 can include one or multiple computers that carry out the processing as described herein.

As shown, computer system 810 of the present example includes an interconnect 811 coupling memory system 812, a processor 813, I/O interface 814, and a communications interface 817.

I/O interface 814 provides connectivity to peripheral devices such as repository 180 and other devices 816 (if such devices are present) such as a keyboard, mouse (e.g., selection tool to move a cursor), display screen 130, etc.

Communications interface 817 enables the analyzer application 140-1 of computer system 810 to communicate over network 190 and, if necessary, retrieve data, update information, etc., from different sources.

As shown, memory system 812 can be encoded with instructions associated with analyzer application 140-1. The instructions support functionality as discussed above and as discussed further below. The analyzer application 140-1 (and/or other resources as described herein) can be embodied as software code such as data and/or logic instructions on a tangible and/or intangible computer readable medium, media, etc. such as memory or on another computer readable medium that supports processing functionality according to different embodiments described herein.

During operation of one embodiment, processor 813 accesses memory system 812 via the use of interconnect 811 in order to launch, run, execute, interpret or otherwise perform the logic instructions of the analyzer application 140-1. Execution of the analyzer application 140-1 produces processing functionality in analyzer process 140-2. In other words, the analyzer process 140-2 represents one or more portions of the analyzer 140 performing within or upon the processor 813 in the computer system 810.

It should be noted that, in addition to the analyzer process 140-2 that carries out method operations as discussed herein, other embodiments herein include the analyzer application 140-1 itself such as the un-executed or non-performing logic instructions and/or data, etc. The analyzer application 140-1 may be stored on a computer readable medium such as a floppy disk, hard disk or in an optical medium. According to other embodiments, the analyzer application 140-1 can also be stored in a memory type system such as in firmware, read only memory (ROM), or, as in this example, as executable code within the memory system 812 (e.g., within Random Access Memory or RAM).

Functionality supported by analyzer 140 and, more particularly, functionality associated with analyzer 140 will now be discussed via flowcharts in FIGS. 9 through 10.

More particularly, FIG. 9 is an example flowchart 900 illustrating operations associated with analyzer 140 according to embodiments herein. Note that flowchart 900 of FIG. 9 and corresponding text below may overlap with and refer to some of the matter previously discussed with respect to FIGS. 1-8. Also, note that the steps in the below flowcharts need not always be executed in the order shown.

In step 910, the analyzer 140 generates an optical signal 115 to pass through a sample 126.

In step 915, the analyzer 140 selects application of each of different optical filters 122 in a path of the optical signal 125 to produce modulated optical signal 125.

In step 920, the analyzer 140 analyzes the modulated optical signal 125 after passing of the modulated optical signal 125 through the sample 126 to detect which of multiple possible target gases are present in the sample 126.

FIG. 10 is an example flowchart 1000 illustrating operations associated with analyzer 140 according to embodiments herein. Note that flowchart 1000 of FIG. 10 and corresponding text below may overlap with and refer to some of the matter previously discussed with respect to FIGS. 1-9. Also, note that the steps in the below flowcharts need not always be executed in the order shown.

In step 1010, the analyzer 140 generates an optical signal 115 in an infrared frequency range.

In step 1015, the analyzer 140 selects application of each of different optical filters 122 in a path of the optical signal 115 to produce modulated optical signal 125. Selecting the different filters 122 can include successive positioning of different optical filters 122 and opaque partitions 220 in the path of the optical signal 115. As previously discussed, each of the different optical filters 122 can be configured to pass a different optical frequency band of the optical signal 115 through the sample 126.

For example, in sub-step 1020, the analyzer 140 disposes a first optical filter such as filter 122-2 in the path of the optical signal 115 for a duration of time. The optical filter 122-2 is configured to pass a first optical frequency energy band of the optical signal 115 through the sample 126.

In sub-step 1030, subsequent to the first duration of time, the analyzer 140 disposes a second optical filter such as filter 122-3 in the path of the optical signal for a duration of time. The second optical filter can be configured to pass a second optical frequency energy band of the optical signal through the sample 126.

In step 1040, subsequent to the second duration of time, the analyzer 100 can dispose a third optical filter such as filter 122-4 in the path of the optical signal 115 for a duration of time. The third optical filter can be configured to pass a third optical frequency energy band of the optical signal through the sample 126.

Based on repeatedly passing the filter 122 in a path of the optical signal 115, the analyzer 140 produce modulated optical signal 125.

In step 1050, the analyzer 140 analyzes the modulated optical signal 125 after passing of the modulated optical signal 125 through the sample 126 to detect which of multiple gases are present in the sample 126.

In step 1060, for each of multiple filters, the analyzer 100 detects an amount of optical energy in the modulated optical signal 125 after passing of the optical energy through the sample 126 for each of the multiple filters 122.

In step 1070, the analyzer 140 determines a concentration of one or more gases present in the sample based on how much of the modulated optical signal 125 is absorbed by the sample 126 at different optical energies.

Those skilled in the art will understand that there can be many variations made to the operations of the user interface explained above while still achieving the same objectives of the invention. Such variations are intended to be covered by the scope of this invention. As such, the foregoing description of embodiments of the invention are not intended to be limiting. Rather, any limitations to embodiments of the invention are presented in the following claims. 

1. A system comprising: an optical source to generate an optical signal; an optical filter assembly including different optical filters in which to filter the optical signal; a controller configured to select sequential application of each of the different optical filters in a path of the optical signal to modulate the optical signal; and an optical analyzer to analyze the modulated optical signal passing through a sample to detect which of multiple gases are present in the sample.
 2. The system as in claim 1, wherein the optical analyzer is configured to determine a concentration of multiple gases present in the sample based on how much of the modulated optical signal is absorbed by the sample at different optical energies, at least two of the multiple gases present in the sample absorbing optical energy in a common frequency band of the modulated optical signal.
 3. The system as in claim 2, wherein the optical filter assembly includes an optical filter to pass optical energy of the optical signal in the common frequency band through the sample to the optical analyzer.
 4. The system as in claim 1, wherein the optical assembly is an optical filter wheel including the different optical filters, the different optical filters of the optical filter wheel separated by opaque partitions that block the optical signal from passing through the sample.
 5. The system as in claim 4, wherein the controller is configured to rotate the optical wheel to each of multiple successive positions including a first position, a second position, and a third position; the first position of the optical filter wheel aligning a first filter of the optical filter wheel with a path of the optical signal enabling the optical signal to pass through the first optical filter and the sample to the analyzer; the second position of the optical filter wheel placing an opaque partition of the optical wheel in a path of the optical signal such that the optical signal does not pass through the sample to the analyzer; and the third position of the optical filter wheel aligning a second filter of the optical filter wheel with the path of the optical signal enabling the optical signal to pass through the second optical filter and the sample to the analyzer.
 6. The system as in claim 1, wherein the multiple filters include a first optical filter and a second optical filter; the first optical filter configured to pass a first optical frequency energy band of the optical signal through the sample to the analyzer; and the second optical filter configured to pass a second optical frequency energy band of the optical signal through the sample to the analyzer, the first optical frequency band being different than the second optical frequency band.
 7. The system as in claim 6, wherein the controller is configured to generate the modulated optical signal based on positioning the first optical filter in a path of the optical signal generated by the optical source and thereafter positioning the second optical filter in the path of the optical signal generated by the optical source.
 8. The system as in claim 1, wherein the sample is a flue sample at least partially derived based on burning of fossil fuels; and wherein the optical analyzer is configured to analyze the modulated optical signal passing through the flue sample to detect which of the multiple gases are present in the flue sample.
 9. The system as in claim 1, wherein the optical source generates the optical signal in an infrared frequency range.
 10. The system as in claim 1, wherein at least one of the multiple optical filters is a reference filter in which none of the multiple gases in the sample absorb optical energy.
 11. The system as in claim 1, wherein the optical analyzer is configured to detect a relative peak optical energy of the modulated optical signal that passes through the sample for each of the filters in the optical filter assembly.
 12. A method comprising: generating an optical signal to pass through a sample; selecting application of each of different optical filters in a path of the optical signal to modulate the optical signal; and analyzing the modulated optical signal after passing of the modulated optical signal through the sample to detect which of multiple gases are present in the sample.
 13. The method as in claim 12 further comprising: determining a concentration of multiple gases present in the sample based on how much of the modulated optical signal is absorbed by the sample at different optical energies.
 14. The method as in claim 12 further comprising: producing the modulated optical signal based on positioning of different optical filters and opaque partitions in the path of the optical signal, each of the different optical filters passing different optical frequency bands of the optical signal through the sample.
 15. The method as in claim 12 further comprising: producing the modulated signal by rotating an optical filter wheel to each of multiple successive positions including a first position, a second position, and a third position: the first position of the optical filter wheel aligning a first filter of the optical filter wheel in the path of the optical signal to enable the optical signal to pass through the first optical filter and the sample to an analyzer that analyzes the optical signal; the second position of the optical filter wheel aligning an opaque partition of the optical wheel in a path of the optical signal such that the optical signal does not pass through the sample; and the third position of the optical filter wheel aligning a second filter of the optical filter wheel in the path of the optical signal enabling the optical signal to pass through the second optical filter and the sample to the analyzer.
 16. The method as in claim 12, wherein selecting application of each of the different optical filters in the path of the optical signal to modulate the optical signal includes: disposing a first optical filter in the path of the optical signal for a first duration of time, the first optical filter configured to pass a first optical frequency energy band of the optical signal through the sample; and subsequent to the first duration of time, disposing a second optical filter in the path of the optical signal for a second duration of time, the second optical filter configured to pass a second optical frequency energy band of the optical signal through the sample.
 17. The method as in claim 12, wherein generating the optical signal includes generating the optical signal in an infrared frequency range.
 18. The method as in claim 12, wherein analyzing the modulated optical signal after passing of the modulated optical signal through the sample includes, for each of multiple filters, detecting an amount of optical energy in the modulated optical signal after passing of the optical energy through the sample for each of the multiple filters.
 19. A computer readable medium having computer code thereon, the medium comprising: instructions for generating an optical signal to pass through a sample; instructions for selecting application of each of different optical filters in a path of the optical signal to modulate the optical signal; and instructions for analyzing the modulated optical signal after passing of the modulated optical signal through the sample to detect which of multiple gases are present in the sample.
 20. The computer readable medium as in claim 19 further comprising: instructions for producing the modulated optical signal based on positioning of different optical filters and opaque partitions in the path of the optical signal, each of the different optical filters passing different optical frequency bands of the optical signal through the sample. 